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 Forum index » How-tos » Surround and Sound Reinforcement
Tuning Sine Sub-bass
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monobass



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PostPosted: Thu May 25, 2006 2:36 am    Post subject: Tuning Sine Sub-bass Reply with quote  Mark this post and the followings unread

Hi,

I'm using a level scaler to tune the sub bass notes of a sinewave so they sound in tune. I can do this pretty well by ear but I wondered if there is just a simple mathematical and accurate approach?

Thanks

Steve

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Afro88



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PostPosted: Thu May 25, 2006 4:36 am    Post subject: Reply with quote  Mark this post and the followings unread

I'm not sure what you mean by tuning the sub bass, but this might be on the right track...

I'm well aware of the phenomenon of sub bass sounding too sharp or flat compared to the rest of the instruments even when it's perfectly in tune according to the synth. Try walking around your room and you may find the tuning changes depending on where you stand. I know deep bass sounds a little sharp on my headphones too.

Bass seems to be very sensitive to reflections and "standing waves" so speaker placement has alot of bearing on how you hear your bass. If you find the place in your room where the bass sounds the most solid (not loud, but solid and well defined), you don't need to worry about bass response again. I did the Mike Stavrou technique of speaker placement (he's the guy that mixed and produced Stevie Wonder etc.) Walking around your room with your friend holding the speaker playing some full and well produced tunes and keeping yourself the same distance from the speaker, keeping an ear out for places where the bass is solid. I haven't had any problems with sub being out of tune or certain notes sounding way too loud or soft since I put my speakers in a solid place. It's amazing how people throw speakers into a room without finding the best place acoustically to put them.
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monobass



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PostPosted: Thu May 25, 2006 4:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Hmmm.. I thought there was some link between the perceived volume of sub bass and pitch?

I don't have any choice over speaker placement. Wish I did!

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mosc
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PostPosted: Thu May 25, 2006 5:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Just a theory - could be wrong - probably is wrong.

A room is a resonant chamber. Based on the dimensions of the room, certain low frequencies will be resonant and other will not be. I'm thinking a room is like an organ pipe or a length of tube use for a brass instrument.

When you blow air into an organ or buzz into a trumpet, a note is generated whose pitch is determined by the physical dimensions and other characteristics of the pipe or tube.

The same for a room, especially at low frequencies. When a bass speaker is playing say 100 Hz and the room has a natural resonant frequency at say 105 Hz, maybe the natural frequency of the room is excited - making the sound appear to be sharp.

Maybe that's why when you walk around the room you hear the pitch move up and down a bit because you are entering different resonant frequency nodes.


[ moving this topic to Surround and Sound Reinforcement - more general than Nord Modular. ]

This doesn't explain the bass sounding sharp in headphones though.

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monobass



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PostPosted: Thu May 25, 2006 5:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah that all makes sense but the effect I'm thinking of is nothing to do with room acoustics if I remember rightly.. definitely something to do with the perceived volume of low bass notes changing the pitch perception.. will have to try and research further.. .I remember reading a webpage about it a couple of years ago.
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Afro88



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PostPosted: Thu May 25, 2006 9:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

I think you're right Mosc, that the room's resonant frequencies override the actual frequency being played. It also sheds light on the different tuning at different volumes problem - if the sound is low, then the room doesn't have much chance to resonate, but if it's loud then it does and changes the pitch.

I'm not sure why sub bass sounds sharp on my headphones... probably because they're crappy headphones!
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ian-s



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PostPosted: Fri May 26, 2006 12:32 am    Post subject: Reply with quote  Mark this post and the followings unread

If we are talking about adding a sine an octave below the bass sound then there are interactions between level and perceived pitch. Like the sub octave waveforms on Roland and Cat synthesisers always sound a little odd to me, phase locked but somehow out of tune. I think upsetting the normal harmonic series fools the ear.
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Blue Hell
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PostPosted: Fri May 26, 2006 6:12 am    Post subject: Reply with quote  Mark this post and the followings unread

Sines seem to be odd to me at higher frequencies as well, when it's just a pure sine and I move my head the pitch seems to change.

Maybe a lack of harmonic clues, or maybe something in the discreteness of the ear's detection mechanism in combination with the head movements. Or maybe damaged stereocilia, got some tinnitus as wel.

Anyway, wikipedia ( http://en.wikipedia.org/wiki/Pitch_%28music%29 ) says :

Quote:

Pitch also depends on the amplitude of the sound, especially at low frequencies. For instance, a low bass note will sound lower in pitch if it is louder.

But that is all it says.

Edit : http://230nsc1.phy-astr.gsu.edu/hbase/sound/pitch.html has some further info.

Edit: http://www.sfu.ca/sonic-studio/handbook/Pitch.html has a graph for the effect of loudness on pitch for some frequencies.

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PostPosted: Fri May 26, 2006 7:43 am    Post subject: Reply with quote  Mark this post and the followings unread

And another interesting read is : http://www.mmk.ei.tum.de/persons/ter/top/pshifts.html
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PostPosted: Fri May 26, 2006 6:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

Interesting stuff, thanks Blue Hell.
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elektro80
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PostPosted: Fri May 26, 2006 6:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

Trivia ( but I am sure someone will figure out why I am posting this )
I briefly mentioned in the WDF Studio Cologne thread ( started by Alexander ) that Stockie and the boys were messing with "complex sine clusters" for a while. This work got a lot of attention at the time. Wink
It might be releveant in an oddball way.. Very Happy

[editor's note: this thread http://electro-music.com/forum/topic-11559.html --mosc]

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carlitos1



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PostPosted: Wed Jun 07, 2006 6:37 am    Post subject: Reply with quote  Mark this post and the followings unread

_ Steve _ wrote:
Hmmm.. I thought there was some link between the perceived volume of sub bass and pitch?


Nearly!

A high pitch (>2kHz) will be perceived to be getting higher if its loudness is increased, whereas a low pitch (<2kHz) will be perceived to be going lower with increased loudness due to the mechanism of the ear. Only at about 85dB is any audio "flat". This is called "Steven's rule" it is crazy but true.

When you next master some tracks get a SPL meter and only EQ when at 85dB. This is the best way to tell how harmonically balanced it is. Even then you only have a few minutes before your ears will tire out.

So nothing is ever really in tune.

"Steven's rule" sometimes breaks down and the shift in perceived pitch travels the other way depending on the instrument.

A square wave can sound flat in pitch next to a sawtooth as it is built out of an odd series of harmonics. It's some of what gives brass its distinctive sound.

I always notice that with a simple bass sound if I crouch down and adjust the cutoff, that when I stand back up it sounds wrong. This is partly to do with "Steven's rule" partly periphonic phase relationships lying about harmonic content and partly the fact that my sampler is low in the rack!

I know all of this can confuse. Telling a musician this is like telling a kid that Santa is not real. We spend most of the time as musicians trying to be in tune just to be told there is no such thing!

440Hz is always 440Hz but middle A will sound different depending on loudness, waveform and localization.

Get yourself a strobe tuner and get really paranoid! Or make sure everything is equally out of tune.
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PostPosted: Wed Jun 07, 2006 6:59 am    Post subject: Reply with quote  Mark this post and the followings unread

That's interesting. I've never heard of Steven's Rule. I tried to find it with Google but no luck. Can you provide a link or something?
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monobass



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PostPosted: Wed Jun 07, 2006 7:03 am    Post subject: Reply with quote  Mark this post and the followings unread

Carlitos1.. yes I think that is what I was thinking about.

I remember doing a patch years ago on my original NM now.. where I think I used a level scaler to change the volume of sub-bass notes and it made them 'seem' more in tune. Will have to experiment. thanks!

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PostPosted: Wed Jun 07, 2006 7:04 am    Post subject: Reply with quote  Mark this post and the followings unread

Try Stevens.. Very Happy
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PostPosted: Wed Jun 07, 2006 7:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Effect of Loudness Changes on Perceived Pitch

A high pitch (>2kHz) will be perceived to be getting higher if its loudness is increased, whereas a low pitch (<2kHz) will be perceived to be going lower with increased loudness. Sometimes called "Stevens's rule" after an early investigator, this psychoacoustic effect has been extensively investigated.

With an increase of sound intensity from 60 to 90 decibels, Terhardt found that the pitch of a 6kHz pure tone was perceived to rise over 30 cents. A 200 Hz tone was found to drop about 20 cents in perceived pitch over the same intensity change.

Studies with the sounds of musical instruments show less perceived pitch change with increasing intensity. Rossing reports a perceived pitch change of around 17 cents for a change from 65 dB to 95 dB. This perceived change can be upward or downward, depending upon which harmonics are predominant. For example, if the majority of the intensity comes from harmonics which are above 2 kHz, the perceived pitch shift will be upward.



form hyperphysics.phy-astr.gsu.edu

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PostPosted: Wed Jun 07, 2006 7:33 am    Post subject: Reply with quote  Mark this post and the followings unread

Wow not much on the web about exactly this but
http://hyperphysics.phy-astr.gsu.edu/Hbase/sound/pitch.html

also Fletcher Munson made some curves other than "equal loudness" that show this phenomenon.

Have you ever had a great sound that no matter how much amplitude you give it you still cant hear it in a mix? Try shifting the pitch! Sometimes things are too in tune. Like trying to look at an individual Zebra within a "gang" of Zebras. This is a common mistake with drummers who try to tune toms to an exact key in a song leaving a weak sound. With drums you nearly always want something to cut across the tuning so that the attack can be heard.
This is why we fanny around with bass sounds so much. Check out some old dub and you will find that to make the bass sound more bassy the low E sting is sometimes tuned quite flat.
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PostPosted: Wed Jun 07, 2006 7:55 am    Post subject: Reply with quote  Mark this post and the followings unread

elektro80 wrote:
Try Stevens.. Very Happy


Yep, that makes a big difference... Very Happy

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